Apparatus for monitoring the action of electromagnetically operated printing hammers

ABSTRACT

An electromagnetically operated print hammer monitoring apparatus is provided in which each hammer has an actuating element to trip an armature associated with the hammer to induce a voltage pulse in the coil of the electromagnet. The actuating element being arranged to trip the armature just as the hammer is about to print a character.

United States Patent Ehrat June 26, 1973 APPARATUS FOR MONITORING THE [56] References Cited ACTION OF ELECTROMAGNETIC/ALLY UNlTED STATES PATENTS OPERATED PRNTING HAMMERS 2,994,071 7/1961 015011 et al 317 010. 6 [75] Inventor: K Eh Z i h S i l d 3,401,362 9/1968 Spiroch et al 335/17 Primary Examiner-L. T. Hix [73] Ass1gnee. Ciba-Gelgy AG, Basel, Sw1tzerl 1nd Att0mey Pierce, Scheffler & Parker [22] Filed: Apr. 6, 1971 21 Appl. No.: 131,637 [57] ABSTRACT An electromagnetically operated print hammer monitoring apparatus is provided in which each hammer has [30] Apphcauon Pnomy Data an actuating element to trip an armature associated Apr. 7, 1970 Switzerland 5122/70 with the hammer to induce a voltage pulse in the coil of the electromagnet. The actuating element being ar- [52] US. Cl 317/123, 3l7/DIG. 6, 335/17 ranged to trip the armature just as the hammer is about [51] Int. Cl. H01h 47/00 to print a character. [58] Field of Search 317/DIG. 5 Claims, 5 Drawing Figures PAIENIEMunzs 191a SiET3N3 APPARATUS FOR MONITORING THE ACTION OF ELECTROMAGNETICALLY OPERATED PRINTING HAMMERS The invention relates to apparatus for monitoring the action of electromagnetically operated printing hammers in printers.

Monitoring means have been described for monitoring the operation of punches in punching equipment for punched tape wherein each punch is associated with an electromagnet having a magnetic circuit which includes the punch when the latter is in position of rest. Each punch is provided with slots so arranged that they change the flux in the magnetic circuit inducing a voltage pulse in the coil of the electromagnet whenever the punch performs a given length of stroke. This voltage pulse indicates that the punch has in fact performed its stroke. This known type of monitoring means cannot be directly applied to a printer. For instance, unlike punching equipment for punched tape the number of hammers is far greater than the number of punches, usually ten times as great. Moreover, since the printing hammers are all crowded into a minimum of space, difficulties arise in finding room for additional electromagnets associated with the increased number of hammers. Furthermore, the aforementioned monitoring means requires the monitored elements to at least partly comprise magnetizable material. Hence this form of monitoring is not applicable to printing hammers made entirely of plastics. Plastics printing hammers are advantageous for several reasons, particularly because of their low weight, their quietness in operation and their low cost.

This invention seeks to overcome these difficulties by providing each printing hammer or a part connected thereto with an actuating element which at or near the print position of the hammer operates an armature associated with the electromagnet operating or releasing the hammer to induce a voltage pulse in the coil of the electromagnet. Hence the electromagnets operating or releasing the hammers are also used to monitor the operation of the hammers, the need for additional monitoring magnets being eliminated.

The invention will be hereinafter more particularly described with reference to the drawings in which FIGS. 1 to 3 are three embodiments of the invention, each schematically shown,

FIG. 4 is a part of FIG. 3 in a different operational state and FIG. 5 is a block diagram of an embodiment of evaluating means associated with the electromagnet of the embodiments shown in FIGS. 1 to 4.

In FIGS. 1 and 2 there is provided a printing hammer l operable by an electromagnet 12. A type carrier 13, an inking ribbon l8 and a paper platen 16 are located in front of the hammer for cooperation therewith. The electromagnet comprises a coil 33 and a core 8. Whenever a current flows through the coil 33 the core 8 attracts an armature 34 which faces the forward end of the core 8 and pivots on a pin 32. When deflected, the free end of the armature 34 propels the printing hammer 1 in the direction of an arrow marked F towards the type carrier 13 to which a type-face 14 is attached. The impact of the printing hammer on the type carrier causes the inking ribbon 18 to be pushed by the typeface 14 into contact with the paper 17 on the platen 16 to produce an impression of the type face on the paper.

Opposite the rear end face of the magnet core 8 is a second armature 7. One end of this armature 7 pivots on a pin 35 and the armature is urged by a spring 39 against the rear end face of the magnet core 8. The printing hammer has a wedge shaped projection 25 positioned on the hammer so as to strike the free end of the armature 7 abruptly deflecting it away from the rear end of the core 8 as the hammer strikes the type carrier 13 during the continued forward motion of the printing hammer I towards the paper platen 16. Owing to the resultant change in magnetic flux at the ends of the coil 33 a peak voltage is induced in the coil which can be used as a monitoring signal. This monitoring signal indicates that the printing hammer 1 has in fact propelled the type face 14 to the paper 17.

In FIG. 2 the armature 34 which operates the printing hammer 1 is connected by a hinge at 36 to a rightangled lever 37. This lever 37 works on a pivot pin 38. When the printing hammer 1 strikes the type carrier 13 the projection 25 strikes the free end of the lever 37, causing the armature 34 that had been attracted by the core 8 to be suddenly thrown off. Hence a voltage peak is induced at the ends of the coil 33, as in the previous example.

In FIG. 3 the shaft of the printing hammer 1 is slidably mounted in guide means 2 and provided with a wedge shaped projection 9 engaged by a hook-shaped end 30 of the armature 7 of an electromagnet 12, the printing hammer being thus kept in a cocked position against the thrust of a compression spring 3. The compression spring 3 exerts thrust in the direction of the arrow marked F towards the platen 16. The armature 7 is tiltable about a hinge 35 and is deflected against the action of a restraining spring 10 about said hinge when the magnet coil 33 is energized, thereby releasing the printing hammer 1 which is propelled by the spring 3 against the type carrier 13. The compression spring 3 is contained in a blind bore 29 in the hammer shaft between the inner end 4 of the bore and an adjustable screw 5 threaded in a rail 6 to permit the spring pressure of the compression spring 3 to be adjusted. The printing hammer 1, the electromagnet 12, the rail 6 and the guide means 2 are all attached to a common frame 11.

The printing hammer 1 is cocked by the back deflection of a cocking element 20 mounted in a bracket 19, a spring 21 on said cocking element engaging a projection 22 on the printing hammer 1 to retract it after a printing stroke against the thrust of the compression spring 3 until the armature 7 again engages the wedgeshaped projection 9. After cocking, the retracting element 20 returns into its former position.

Leaf springs 15 supporting the type carrier 13 are attached to a deflectable carrier 23 which is connected by a coupling link 24 to the cocking element 20, and which is therefore deflected when the printing hammer l is being cocked, pulling the type carrier 13 away from the platen 16, to uncover the printed text on the paper 17 to permit it to be seen. The hammer cocking and type carrier retracting device is preferably common to all the printing hammers and the type carriers.

Preferably the armature 7 is a two armed lever, one arm being formed with a hook-shaped end 30, whereas the other arm has an upward sweep at its end 31. This upswept end 31 is located in the path of a ramp 25 on the printing hammer 1. At the same time as the printing hammer l strikes the type carrier 13 the upswept end 31 of the armature 7 rides up the ramp deflecting the armature about its hinge 32 and thus pulling it away from the electromagnet 12. The result is the generation of a voltage pulse at the terminals of the magnet coil and this pulse is used to provide a monitoring signal indicating that the printing hammer has completed its stroke and that the impression has been made.

In order to avoid excessive force in deflecting the armature 7 away from the magnet the current for energizing the magnet 12 is so controlled tat the retaining force of the magnet at the instant of armature withdrawal is merely a fraction of the initial force of attraction of the magnet. For instance, this retaining force may preferably be only one-fifth to one-tenth of the initial force of attraction. The magnet coil 33 may comprise two windings of which one is for energizing the magnet and the other for the generation of the peak induction voltage.

FIG. 4 shows the printing hammer 1 at the instant of striking the type carrier 13. The armature 7 is still being held by the magnet, but during the continued movement of the printing hammer 1 towards the platen 16 it is forcibly pulled away from the magnet by riding up the ramp 25. When the printing hammer is cocked in a direction opposite to that indicated by the arrow F, the armature 7 will be kept in released position by the pull of the spring 10.

A monitoring device for a printing hammer is shown in FIG. and comprises a bistable storage element 26 and two amplifiers 27 and 28. The operating signal for a printing hammer is applied to its associated storage element 26 which in response thereto changes state. Consequently the magnet coil 33 is energized via the amplifier 27 and the printing hammer l is released (FIG. 3). The voltage pulse which is induced at the end of the hammer stroke is amplified in suitable manner in the amplifier 28 and resets the storage element 26. Before a fresh hammer operating signal is applied to the storage element 26 a check is carried out to determine if the storage element has been reset by the induced voltage pulse and whether the printing hammer has completed its movement.

In a line printer the storage elements 26 of the printing hammers together constitute a shift register, the hammer operating signals for each printing cycle being applied sequentially to the shift register. When the selected hammers have been released the induced peak voltages restore the corresponding storage elements to their former states. For example, whilst the printing hammers are being cocked a complete shift through the shift register may be used to check whether all the hammer operating signals have been cleared. For instance, should one of the storage elements still be in the operate state a warning signal may be produced.

What is claimed is:

1. Apparatus for monitoring the operation of printing hammers in printers, each hammer being operable by an electromagnet having a coil and an armature wherein each printing hammer is provided with an actuating element which in the vicinity of the point of motion reversal of the hammer operates the armature associated with the electromagnet to induce a voltage pulse in the coil of the electromagnet, and evaluating means coupled to said coil to indicate that the hammer has made a printing stroke.

2. Apparatus according to claim I, wherein said magnet armature is a lever and said actuating element comprises a wedge-shaped projection on said hammer and which adjacent the point of hammer motion reversal deflects the magnet armature relative to the core.

3. Apparatus according to claim I, wherein the magnet armature is one arm of a two-armed lever, the other arm extending into the path of the actuating element.

4. Apparatus according to claim 3, wherein each said hammer includes a holding member and said apparatus further includes a compression spring, means holding the printing hammer in a normal cocked position against the thrust of said spring by one arm of said lever, said one arm having a hook-shaped end engaging said holding member said one arm being deflected to operate the printing hammer when the state of excitation of the magnet is changed, the actuating element comprising a ramp cooperation with the other arm to restore the two-armed lever to its position of rest when the printing hammer reaches the point of motion reversal.

5. Apparatus according to claim 4, including a spring attached to said other arm to oppose the force of the magnet on said one arm but which develops a force less than the force of attraction of the magnet, and that the current for energizing the magnet is so changed in time that the retaining force of the magnet on said one arm at the instant said other arm causes said one arm to be forcibly retracted from the magnet in the region of the point of hammer motion reversal is in the range of onefifth to one-tenth of the initial force of attraction of the 

1. Apparatus for monitoring the operation of printing hammers in printers, each hammer being operable by an electromagnet having a coil and an armature wherein each printing hammer is provided with an actuating element which in the vicinity of the point of motion reversal of the hammer operates the armature associated with the electromagnet to induce a voltage pulse in the coil of the electromagnet, and evaluating means coupled to said coil to indicate that the hammer has made a printing stroke.
 2. Apparatus according to claim 1, wherein said magnet armature is a lever and said actuating element comprises a wedge-shaped projection on said hammer and which adjacent the point of hammer motion reversal deflects the magnet armature relative to the core.
 3. Apparatus according to claim 1, wherein the magnet armature is one arm of a two-armed lever, the other arm extending into the path of the actuating element.
 4. Apparatus according to claim 3, wherein each said hammer includes a holding member and said apparatus further includes a compression spring, means holding the printing hammer in a normal cocked position against the thrust of said spring by one arm of said lever, said one arm having a hook-shaped end engaging said holding member said one arm being deflected to operate the printing hammer when the state of excitation of the magnet is changed, the actuating element comprising a ramp cooperation with the other arm to restore the two-armed lever to its position of rest when the printing hammer reaches the point of motion reversal.
 5. Apparatus according to claim 4, including a spring attached to said other arm to oppose the force of the magnet on said one arm but which develops a force less than the force of attraction of the magnet, and that the current for energizing the magnet is so changed in time that the retaining force of the magnet on said one arm at the instant said other arm causes said one arm to be forcibly retracted from the magnet in the region of the point of hammer motion reversal is in the range of one-fifth to one-tenth of the initial force of attraction of the magnet. 